The influence of animal characteristics immediately post-partum on the
voluntary feed intake and nutrient utilization for milk production during 24
weeks of lactation was studied in two trials, one involving cows and the other
cows plus heifers. The influence of eating behaviour on daytime voluntary feed
intake was studied in early lactation (weeks 1-8) using 33 animals and in middle
and late lactation with 40 animals.
It was shown that environmental factors (years and months of calving), parity,
calving liveweight, calving condition score, milk yield in lactation week 2 and
liveweight change within the period of lactation explained the following
proportion of the variation in voluntary feed intake 41.3-60.1 and 48.0-74.996;
in milk yield 23.3-58.9 and 33.3-91.5%; in energy balance 30.1-69.0 and
28.6 - 50.696; gross efficiency 25.5-69.0 and 35.5-62.2%; in net efficiency 27.5-
68.0 and 32.6-42.9% and in nitrogen efficiency 19.3-48.1 and 20.8-58.9% for
different stages of lactation in Trials 1 and 2 respectively.
In the behaviour study the animals were found to have a two-peak pattern of
eating; the hour immediately after fresh feed offering and milking. Fifty per
cent of the within day variation between animals in voluntary feed intake was
due to differences in the time spent eating.
The selection of animals for high milk yields has resulted in animals with high
appetites and efficiency, and the ability to mobilize body reserves in early
lactation. Animal to animal variation in the mobilization and storage of body
reserves was the main cause of differences between animals in energetic and
nitrogen efficiency for milk production. Calving condition score was not related
to voluntary feed intake or to nutrient utilization after lactation week 12; and
milk yield. It was concluded that calving condition score can be manipulated
to improve voluntary feed intake without affecting milk yield. Areas of further
research are suggested.